This invention relates to internal combustion engines and particularly to such engines having a variable compression ratio mechanism and a control system therefor.
The fuel economy of an internal combustion engine is related to the compression ratio of the combustion chamber. The compression ratio of the engine is the combustion chamber volume at top dead center (TDC) divided by the combustion chamber volume at bottom center (BDC). In most spark ignition engines, the compression ratio is a constant value in the range of 9.0 to 11.0. The use of a constant compression ratio is generally satisfactory; however, a variable compression ratio can improve the economy and performance by increasing the compression ratio at light loads and decreasing the compression ratio at heavy loads.
It is, therefore, advantageous to employ a variable compression ratio, and systems for providing this feature have been proposed in many publications. U.S. Pat. Nos. 5,165,368 and 5,960,750 both suggest such mechanisms and controls therefor. European Patent Application 0 184 042 also proposes a variable ratio mechanism. These systems utilize an eccentric bearing that rotatably supports the piston rod on the engine crankshaft. In the European Patent Application, the eccentric bearing is continuously rotated relative to the crankshaft and the piston rod bore in which the bearing is positioned. This relative rotation increases the friction within the engine and therefore negatively affects the fuel economy.
The variable compression ratio is also important in the success of a Homogeneous Charge Compression Ignition (HCCI) engine. These engines operate with reduced emissions at relatively high fuel economy rates. The HCCI engine needs high compression ratio to provide initial ignition of the fuel air mixture in the combustion chamber. However, the high pressure rise normally resulting from combustion must be tempered. This can be accomplished with a variable compression ratio mechanism.
It is an object of the present invention to provide an improved control mechanism for a variable compression ratio in an internal combustion engine.
In one aspect of the present invention, a variable compression ratio control maintains the eccentric crankshaft bearing stationary relative to the crankshaft when the compression ratio is constant. In another aspect of the present invention, the crankshaft bearing is rotated at a speed equal to the crankshaft speed when the compression ratio is constant. In yet another aspect of the present invention, the eccentric crankshaft bearing is rotated relative to the crankshaft during adjustment of the compression ratio.
In still another aspect of the present invention, the relative position of the eccentric crankshaft bearing is controlled by a plurality of meshing gears, one of which is secured for common rotation with the crankshaft bearing. In yet still another aspect of the present invention, a second of the plurality of meshing gears has both internal and external teeth formed thereon. In a further aspect of the present invention, the inner teeth of the second gear mesh with the gear on the crankshaft bearing and the outer teeth mesh with an engine-driven gear. In a yet further aspect of the present invention, the engine-driven gear is drivingly connected with the engine crankshaft through a differential gear mechanism that is controllable to vary the speed of the engine-driven gear during a change of the compression ratio. In a still further aspect of the present invention, the engine-driven gear is equipped with a lost motion mechanism, in the form of a spring, which permits a temporary change in the compression ratio during either the compression stroke or the power stroke.